You mentioned stripping out some of the markup. Does that mean you have Sigil? .

Thanks Barb-B, I am familiar with and do use Sigil but in this case I used Tag Stripper to strip a HTML file to its bare bones.

I thought Calibre was not behaving as described bu it was just ignorance about how CSS files worked on my part. Unfortunately until I retire next year I have only limited time to spend acquiring such knowledge.